A hydrotreating catalyst may be defined as any catalyst composition which may be employed to catalyze the hydrogenation of hydrocarbon feedstocks, and most particularly to hydrogenate particular components of the feed stock such as sulfur-, nitrogen- and metals-containing organo-compounds and unsaturates. A hydrocracking catalyst may be defined as any catalyst composition which may be employed to crack massive and complex petroleum derived molecules to attain smaller molecules with the concomitant addition of hydrogen to the molecules. A tail gas catalyst may be defined as any catalyst which may be employed to catalyze the conversion of hazardous effluent gas streams to less harmful products, and most particularly to convert oxides of sulfur to hydrogen sulfide which can be recovered and readily converted to elemental sulfur.
Catalyst compositions for hydrotreating and/or hydrocracking or tail gas treating are well known to those of ordinary skill in the art and several are commercially available. Metal oxide catalysts which come within this definition include cobalt-molybdenum, nickel-tungsten, and nickel-molybdenum supported usually on alumina, silica and silica-alumina, including zeolite, carriers. Also, transition element catalysts may be employed for these purposes. In general catalysts comprising at least one element selected from V, Cr, Mn, Re, Co, Ni, Cu, Zn, Mo, W, Rh, Pd, Pt, Ag, Au, Cd, Sn, Sb, Bi and Te have been disclosed as suitable for these purposes.
For maximum effectiveness the metal oxide catalysts are converted at least in part to metal sulfides. The metal oxide catalysts can be sulfided in the reactor by contact at elevated temperatures with hydrogen sulfide or a sulfur-containing oil or feed stock. However, it is advantageous to the user to be supplied with metal oxide catalysts having sulfur incorporated therein. These presulfurized catalysts can be loaded into a reactor and brought up to reaction conditions in the presence of hydrogen causing the sulfur to react with hydrogen and the metal oxides thereby converting them into sulfides without any additional process steps being needed. These presulfurized catalysts provided an economic advantage to the plant operator and avoid many of the hazards such as flammability and toxicity, which are encountered when using hydrogen sulfide, liquid sulfides, polysulfides and/or mercaptans to sulfide the catalysts.
The use of high boiling oils, such as vacuum gas oils, and hydrocarbon solvents to aid the incorporation of sulfur into a catalyst is taught in U.S. Pat. No. 4,943,547, issued Jul. 24, 1990.
Hydrotreating catalysts have been presulfurized by incorporating sulfur compounds into the porous catalyst prior to hydrotreating a hydrocarbon feedstock. For example, U.S. Pat. No. 4,530,917, issued Jul. 23, 1985, to Berrebi discloses a method of presulfurizing a hydrotreating catalyst with organic polysulfides.
U.S. Pat. No. 4,117,136, issued Dec. 4, 1979, to Herrington et al discloses a method of catalyst presulfurizing wherein a catalyst is treated with elemental sulfur. Hydrogen is then used as a reducing agent to convert the elemental sulfur to hydrogen sulfide in situ.
U.S. Pat. No. 4,089,930, issued May 16, 1978, to Kittrell et al discloses the pretreatment of a catalyst with elemental sulfur in the presence of hydrogen.
Prior art ex-situ methods of presulfurizing supported metal oxide catalysts have suffered from excessive stripping of sulfur upon start-up of a hydrotreating reactor in the presence of a hydrocarbon feedstock. As a result of sulfur stripping, a decrease in catalyst activity or stability is observed.